Plumbing leaks and pressure...? October 28, 2011, 01:26:24 pm Yahoo Message Number: 126247I have a question for any experienced plumbers out there. I had always assumed that our RV appliances eventually developed leaks due mostly to the increased line pressure when the water heater heats up. Over the years we've had our '83 FL, I have had numerous leaks, particularly from the water inlet/regulator/check valve unit and the water pump. It concerned me that the only pressure relief is on the water heater and set to 150 psi, way above what I feel the plumbing system should have to sustain. But, while planning a solution, I did the actual pressure calculation for a water heater heating from 70F to about 150F, and it seems the pressure increase would only be about 5 psi - insignificant. So, my question is: am I overlooking something? Is there anything else that could cause the pressure to spike, or am I simply looking at age-deterioration issues. Note that we NEVER actually hook up to shore-water - we always just fill the tank.Steve
Re: Plumbing leaks and pressure...? Reply #1 – October 28, 2011, 06:04:41 pm Yahoo Message Number: 126250Hi Steve, Everyone has a water heater, and most of us hook up to shore water, at least ocasionally, but most don't have any problem with leaks. My only leak came from a 10 year old water pump that I think suffered some freeze damage, not bad for 14 seasons of about 3 months each year, 170,000 miles. Now, it might be the older units like yours used different pipes, fittings and other things that are more prone to problems (mine is a 1998).Eric
Re: Plumbing leaks and pressure...? Reply #2 – October 28, 2011, 06:08:21 pm Yahoo Message Number: 126251Steve, As anyone who has had a waterlogged water heater, i.e. one with no air pocket, would testify pressure relief valves get activated. (The Mothership's owner's manual tell you how to correct the problem.) There's no question that 150 PSI can be reached at the water heater. Here's a link to an article that indicates that a 40 gallon tank when heated from 70 degrees F to 180 degrees F it will expand a half a gallon. Water is not known to be compressible. If the container does not expand and there's no air pocket to take up the expansion of the water, the pressure generated would undoubtedly rupture the water heater tank if the relief valve was not in place. If you're calculations were accurate, properly working pressure relief valves would never open.Alex Rutchka, (not a plumber ) SE #4 '05 MB
Re: Plumbing leaks and pressure...? Reply #3 – October 28, 2011, 07:01:57 pm Yahoo Message Number: 126254QuoteAs anyone who has had a waterlogged water heater, i.e. one with no air pocket, would testify pressure relief valves get activated. (The Mothership's owner's manual tell you how to correct the problem.) There's no question that 150 PSI can be reached at the water heater. Here's a link to an article that indicates that a 40 gallon tank when heated from 70 degrees F to 180 degrees F it will expand a half a gallon. Water is not known to be compressible. If the container does not expand and there's no air pocket to take up the expansion of the water, the pressure generated would undoubtedly rupture the water heater tank if the relief valve was not in place. Alex, if water does not compress, then reflexively it should not expand - but I'd like to read the link - you forgot to post it! Thanks for responding. BTW, my calculation assumed there is an air bubble, and that water does not expand significantly - i.e. the bubble volume remains the same.Steve
Re: Plumbing leaks and pressure...? Reply #4 – October 28, 2011, 08:30:27 pm Yahoo Message Number: 126255Steve,Sorry about the missing link on water expansion. Here it is: http://www.watts.com/pages/learnAbout/thermalExpansion.aspAnd by water not compressing I mean that, at a given temperature, if you squeeze it, it refuses to take up less space (volume). Changing its volume with temperature is another matter.Alex
Re: Plumbing leaks and pressure...? Reply #5 – October 29, 2011, 02:25:24 am Yahoo Message Number: 126260QuoteAnd by water not compressing I mean that, at a given temperature, if you squeeze it, it refuses to take up less space (volume). Changing its volume with temperature is another matter.Alex Thanks for the link, Alex. However, if heat causes water to expand, then increasing pressure will cause it to compress - giving off heat. Of course, this factoid has no practical use in this case. The expansion could significantly reduce the already small air bubble, increasing the pressure much more than my simplified calculation found. I'm planning to install a separate pressure relief valve at 75 psi.Steve
Re: Plumbing leaks and pressure...? Reply #6 – October 29, 2011, 11:07:23 am Yahoo Message Number: 126263Suburban has a procedure for maintaining an air pocket in the heater, so there is room for expansion; alternatively, they suggest installing an expansion or accumulator tank in the cold water line. http://www.rvcomfort.com/suburban/service/water_questions.phpI don't recall if you've tried the air pocket method, but it's easy to try if you haven't.Eric
Re: Plumbing leaks and pressure...? Reply #7 – October 29, 2011, 01:39:51 pm Yahoo Message Number: 126266Steve, let me provide the results of some testing I did. First, I used my water pump. I was not connected to shore water. Second, overnight temps were in the 40's but my water tank, being inside and full, probably was in the high 60's to low 70's in the morning. My 2008 rig had the old ShurFlo Extreme 5.7 pump. I connected a pressure meter to my system and made sure I had "burped" my water heater so I had an appropriate air pocket there. I turned on the pump after burping the heater. The meter showed 80 psi. I turned on the water heater. As the water temp came up, so did the pressure, finally reaching 150 psi. At that point, my system leaks under the bathroom sink. I do not get quite to the point where the heater pressure relief opens. I solved my problem in two ways. First, I use an accumulator to reduce the pressure spike by providing more expansion space. Second, I turn off the pump and run a glass of water before starting the heater in the morning, thus reducing the in-line pressure.Should this be necessary? No. But it works.Ken F in NM
Re: Plumbing leaks and pressure...? Reply #8 – October 29, 2011, 05:07:13 pm Yahoo Message Number: 12626780 psi from the water pump seems unusually high. I suspect much lower, say 50 psi, would be completely adequate for anything but a really large rig with a dishwasher, washer, etc.Eric
Re: Plumbing leaks and pressure...? Reply #9 – October 29, 2011, 06:08:19 pm Yahoo Message Number: 126268Quote "I connected a pressure meter to my system and made sure I had "burped" my water heater so I had an appropriate air pocket there. I turned on the pump after burping the heater. The meter showed 80 psi."Ken F in NM Please tell us the exact point where you "connected" the pressure meter. You must to have had to open the system in order to do this, no? I find that I can reduce or eliminate the weeping at the pressure relief valve if I turn off the pump or the campground water supply and then open a hot water valve prior to lighting the water heater.Steve S. Lazy Bones & Jiggs
Re: Plumbing leaks and pressure...? Reply #10 – October 29, 2011, 07:22:08 pm Yahoo Message Number: 126269Thanks Ken, Eric, and Steve. Your experiences mirror mine, but my worst leaks have occurred at the city water inlet, causing un-noticed damage over time to the interior wall behind the kitchen counter. This is due to the Shurflo plastic inlet/pressure-regulator/check-valve that LD wisely no longer uses. The Valterra inlet lacks the pressure regulator, but is metal and brass and pretty much immune to this issue. I will be converting over, and installing a 75 psi pressure relief valve to route the overflow back to the water tank.Steve
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